Winter annual legume cover crops can reduce nitrogen (N) fertilizer requirements and provide a water-conserving mulch to a subsequent crop. A two-year study was designed to test cover crops of rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), and big/lower vetch (Vicia grandiflora Scopoli) for their ability to produce N and to conserve soil water for a succeeding corn (Zea mays L.) crop. We measured the cover crops' biomass, N yield, carbon (C) to N ratio, and influence on a subsequent corn crop grown under two tillage regimes (disk tillage or no-till). Nitrogen content in cover crop biomass at time of corn planting ranged from 37 to 187 kg/ha. Pure stands of hairy vetch and a mixture of hairy vetch plus bigflower vetch had generally higher N yields, and rye was lowest. Rye growing in association with hairy vetch had lower C:N ratios than rye growing alone. Legume C:N ratios remained generally unchanged from earlier (disked) to later (herbicide) kill dates, but total N and biomass typically increased in the last 2 to 3 weeks before corn planting. Soil water retention was affected by tillage in some cases; no-till was superior to disk incorporation in each case where there was a tillage effect. Cover crops with greater biomass resulted in greater soil water retention. Among cover crops, uptake ofNby corn was greater from hairy vetch or hairy vetch plus bigflower vetch mixture. Biological immobilization of N appeared to be reducing N uptake by corn grown in rye residues. Corn in nonlegume plots fertilized with 140 or 210 kg N/ha took up more N than corn following legumes, but there was no corresponding yield increase. Corn biomass yields following the cover crops ranged from 8.6 to 18.0 Mg/ha with no additional fertilizer N. In the second year of the study, average corn yields following hairy vetch (15.3 Mg/ha) or hairy-bigflower vetch mixtures (16.4 Mg/ha) were not statistically different from corn yields produced by a 140 kg N/ha fertilizer rate (17.4 Mg/ha). These results suggest N from a legume cover crop can replace or substantially reduce fertilizer N requirements in corn production systems in the Appalachian region.

The logic of the Clean Development Mechanism (CDM) and other such ‘carbon (C) offsets’ rests on the notion that the opportunity cost of reducing C emissions is lower in developing countries, creating opportunities for mutually beneficial C trading. While the CDM may offer significant gross financial benefits, there has been little analysis of the opportunity costs of foregone resource exploitation and development opportunities. In addition to assessing the potential for net benefits, this paper also considers the practical implications for design and implementation of C offsets for forest conservation and agroforestation in Indonesia. Virtually nothing is known about these administrative factors, and their associated costs, which can also play a decisive role in feasibility of C offset schemes. Data are from field studies in the lowlands of the Indonesian island of Sumatra, where forests and derived land uses are broadly representative of the lowland humid tropical rainforest systems of insular South-East Asia. These data are the basis for assessing the trade-offs between natural forest protection for C sequestration and conversion to other land uses to meet national development objectives that directly affect people's livelihoods. Carbon stocks are analyzed in terms of ‘time-averaged’ C, an indicator developed for this project. Opportunity costs of land-use alternatives are estimated using standard techniques for economic assessment of investment projects in developing countries. The study finds that imputed timber values are a significant share of the opportunity costs of forest conservation, even for conservative estimates of timber prices. The question of compensating for these foregone values raises complex questions regarding the political economy of Indonesia, since property rights over these resources are highly contentious. These controversies over property rights are also examined within the context of recurrent smoke pollution from land fires in Indonesia, that (among other problems) contribute to greenhouse gas emissions. This smoke is symptomatic of deeper political and institutional problems that raise questions about the permanence of C storage through land-use practices in Indonesia. In comparison to forest conservation, C offsets through agroforestation seem more feasible in Indonesia because property rights over timber from planted trees would be easier to establish and enforce than property rights over timber from natural forests. Although results in this paper look promising, there is still much to be learned about implementation costs, even for the ‘easier’ case of agroforestation.

Research plots that are large enough to accommodate regular farm machinery are thought to contain too much field variation to allow reliable interpretation of experimental results. This study was conducted to determine whether experimental error was controlled on a wide variety of agricultural field trials that used plots larger than normally used by researchers. The investigation included trials conducted on an experiment station and trials conducted on actual commercial farms. The planning and management of the experiments ranged from those completely conducted by university researchers to those completely done by farmers.

The level of experimental error in all the trials was well within the limits normally accepted by researchers in agronomy. Plots ranging in length from 125 to 1200 feet and as wide as one or two passes of standard farm machinery gave experimental results that were statistically sound. Statistical requirements for randomization and replication were all met.

The ability to use large plots and farmer participation enhances the testing of new technology on farms. This leads to new opportunities to test crop production factors in a systems setting under actual farm conditions. The statistical reliability of the on-farm designs analyzed in this study should increase cooperation among researchers, extension workers, and farmers in research activities.

The energy crisis of the late 1970's has raised the question of the wisdom of depending upon fertilizer nitrogen as the primary source of N input into crop production systems. While present and past price structures have favored fertilizer-N over biologically fixed N, there are a number of other benefits of legumes in a cropping system in addition to their effects on N availability. Among these are less potential for environmental degradation and improved soil physical conditions and water relations, but it is difficult to assign economic value to many such benefits. In addition to the economics of the present price structure, disadvantages of using legumes could include reduced total production and increased need for livestock in a farming enterprise (these could be considered assets from some aspects). Legumes are presently used in shortterm rotation, such as corn-soybean, or in continuous corn with a legume winter cover crop. These systems are finding widespread use and offer the producer many benefits, as well as helping to solve several major environmental problems associated with N use in agriculture.

There is a growing interest in the use of soil microbial inoculants as an alternative biological approach to a) improve soil quality, b) enhance the growth, yield and quality of crops, and c) reduce the inputs of chemical fertilizers and pesticides in agriculture worldwide. One such product that has received considerable attention, is Effective Microorganisms or EM; it consists of mixed cultures of beneficial microorganisms. A long-term field experiment was conducted at Faisalabad, Pakistan to determine the agronomic and economic merits of EM in a rice-wheat cropping system. Treatments were applied in a randomized complete block design that included: control (untreated); recommended chemical fertilizer (NPK); green manure (GM); farmyard manure (FYM); Effective Microorganisms (EM) alone; NPK + EM; GM + EM; and FYM + EM. Significantly higher grain and straw yields for both crops were obtained with NPK alone, with other treatments in the following order: NPK > GM > FYM > EM. However, when fertilizer and organic amendments were combined with EM, higher grain and straw yields were obtained for each crop following the same order, i.e., NPK+EM > GM+EM > FYM+EM. The GM+EM treatment produced grain and straw yields for each crop that approached those for NPK alone. In all cases, the grain and straw yields from EM alone were higher than the controls. With few exceptions, EM applied in combination with NPK, GM and FYM caused a significant increase in nutrient uptake by the grain and straw of each crop. The uptake of NPK by both crops was higher for EM alone than for the controls. A comparative economic analysis of the treatments showed a significantly higher net return due to EM. The average net profit from rice and wheat production using EM was $44.90 ha−1 and $62.35 ha−1, respectively. The study indicates that EM can enhance maximum economic yields in a rice-wheat rotation and also improve soil productivity when applied with organic amendments.

The mining of sand and gravel deposits and excavation oftopsoil in urban areas have left extensive tracts of exposed subsoils that do not support plant growth because of adverse soil chemical and physical properties. Such degraded and marginal soils, or spoils, are infertile, low in organic matter, often acidic, and subject to severe erosion and surface runoff Many of these lands are owned by small and part-time farmers who wish to restore their aesthetic value and agricultural productivity. Research has shown that with liming and the proper use of organic amendments such as animal manures and sewage sludge compost, these lands can be restored to a high level of productivity in as little as three years. The methods and techniques for improving the productivity of marginal soils described in this paper can be of considerable benefit to some farmers in developed and developing countries where there is no other choice but to farm marginal soils because of the lack of highly productive agricultural lands. With increased efforts to restore the productivity of degraded and marginal soils through the use of organic amendments, conservation tillage, and crop rotations, future research should address the effect of best management practices on crop yields, the nutritional quality of crops, and the bioavailability of plant nutrients to both animals and humans.

Annual legumes and mixtures of annual legumes and grasses can perform several functions as understory cover crops in pecan orchards, such as providing nitrogenrich organic matter to improve soil fertility, or by sustaining lady beetles and other arthropods that may aid the biological control of pecan pests. Remaining questions concern selection of appropriate plant materials; whether to use cover crops singly or in mixtures; how to ensure reseeding as well as a substantial N contribution; whether, when, and how to use mowing and tillage; and fertilization options. Different considerations apply when dealing with cool- vs. warm-season cover crops. With minor adjustments, growers could adapt present cultural practices to include cool-season cover crops. These could be used throughout the orchard, by establishing appropriate self-reseeding species and avoiding both excessive mowing and indiscriminate placement of N-rich fertilizers. Within alleys, alternating 2-m strips of cool-season cover crops could be tilled in mid to late April or allowed to mature. The tilled strips would supply N to pecan trees immediately, whereas the adjoining untilled (remnant) strips could be mowed after seed is mature, to ensure dispersal of seed and reestablishment of cover crops over the entire alley. Cool-season annual legumes that die or are killed in late spring will probably furnish N and other nutrients at a suitable time, particularly in orchards with sprinkler irrigation. Warm-season cover crops, if desired, should be restricted to alleys to reduce possible competition with pecan. Alleys provide better illumination than do tree rows during periods when pecan trees are in leaf, and the tillage mentioned above will encourage emergence of warm-season cover crops. If these die or are killed in late summer or early fall, timing of N release may not be optimal, in the absence of adequate irrigation. Many options and tradeoffs need to be explored before choosing a cover-crop system. Attimes, several objectives may appear to conflict, and even delicately-managed mixtures of species may not fulfill all the desired functions.

The Northwest Wheat Region is a contiguous belt of 3.3 million ha in Idaho, Oregon and Washington. Its climate varies from subhumid (<650 mm annual precipitation) to semiarid (<350 mm), with more than 60% of the annual precipitation occurring during the winter. Winter wheat yields range from a high of 8 t/ha in the wetter zones to a low of 1.5 t/ha in the drier zones. Winter wheat is grown in rotation with spring cereals and pulses where annual precipitation exceeds 450 mm; winter wheat-fallow prevails where annual precipitation is less than 330 mm. Tillage practices are designed to maximize infiltration and retention of water through soil surface and crop residue management. Because of the combination of winter precipitation, steep topography, and winter wheat cropping, much of the region is subject to a severe water erosion hazard, accentuated by freeze-thaw cycles that increase surface runoff and weaken the soil structure. Wind erosion is a major problem in the drier zones, where cover is less and soils are higher in sand. Residue management, primarily through reduced tillage and no-till systems, is the first defense against both wind and water erosion, but yields often are higher with conventional intensive ti llage. Factors that limit yields with conservation farming include weed and disease problems and th e lack of suitable tillage and seeding equipment. Conservation strategies must shift from relying on traditional tillage methods to development of complete no-till systems. Spring cropping as a replacement for winter wheat also needs to be investigated. In some cases, tillage for water conservation must be made compatible with tillage for erosion control.

Vesicular-arbuscular mycorrhizal (VAM) fungi colonize plant roots and the surrounding bulk soil. They transport mineral nutrients from the soil to the plant and carbon compounds from the plant to the soil, and have pervasive effects on plant form and function and on the composition of the soil microbiota. This experiment evaluated VAM effects on plants and soil to determine if VAM fungi mediate a relationship between changes in seed yield and soil aggregation. In a pot experiment with peas, an isolate of the VAM fungus Glomus mosseae (Nicol & Gerd.) Gerd. and Trappe did not significantly affect seed yield (8%), but improved soil aggregation by 400% in one soil, a gray silt-loam high in organic matter (OM) and phosphorus. In another soil, a yellow clay-loam low in OM and phosphorus, seed yield was enhanced significantly (57%), but there was only a small change (50%) in aggregation. The results suggest that carbon allocation between the plant (measured as seed yield) and the soil (measured as the formation of water-stable aggregates) is influenced by this VAM fungus. The soil appeared to gain carbon at the expense of carbon lost by the plant Mycorrhizal fungi thus seem to affect two biologically controlled aspects of sustainable agriculture: plant production and soil quality.

Cover crop performance depends largely on management factors that must be customized to particular farm situations and, therefore, is suited for on-farm research, with farmers involved in both management and evaluation. Cover crop sequences that were successful in a research station study were tested over a variety of soils and management strategies in collaboration withfarmers. The two-year cover crop sequences consisted of a short-season crop followed by a cover crop in year one and corn in year two. The cover crops themselves were evaluated by their agronomic and economic performance and their acceptance by farmers. Four cover crop systems (companionseeded red clover, sequentially seeded hairy vetch, sequentially seeded oat, and fallow) were compared for ground cover, above-ground biomass and above-ground nitrogen yield, subsequent corn grain yield, and N fertilizer replacement value (N-FRV). Cover crops were essential for erosion control following vegetable crops and tillage, but were not necessary following small grains. Companion-seeded red clover produced the most ground cover, yielded up to 133 kg N/ha, and had a higher average N-FRV than sequentially seeded hairy vetch on sandy loam soils, but was not preferred by farmers who harvested small grain straw as well as grain. Sequentially seeded hairy vetch gave excellent cover when no-till seeded, produced more than 125 kg N/ha in half the siteyears, and had a higher average N-FRV than companion-seeded red clover on silt loam soils. First-year N-FRV for the legume cover crops averaged 67 kg N/ha over both soil types. The participating farmers indicated that their decisions to adopt cover crops would be based primarily on their need for ground cover, and secondarily on the profitability of using cover crops as an N source. However, when valued solely as an N source for the next year's crop (and not for any potential long-term benefits), cover crops were not an economical alternative to N fertilizer. We suggest focusing future cover crop research and extension efforts on outreach to farmers growing crops that do not provide sufficient ground cover, such as short-season vegetable crops, and optimizing the cover crop system to maximize its erosion control benefits and increase its profitability over N fertilizer.

Few plant breeding programs involve attempts to develop varieties specifically adapted to low-input cropping systems. Plant breeders generally select varieties in highly fertile, weed-free, densely seeded environments. However, alleles needed for achieving maximum yield in low-input environments often differ from those required in highinput conditions. Thus, when effective selection can be undertaken under low-input conditions, breeding programs specifically targeted at low-input environments should produce the best varieties for those environments. Experimental protocols for identifying such situations are described in this review. These involve (a) testing breeding lines under low- and high-input conditions, (b) estimating both the degree to which yields from the two types of environment are controlled by the same alleles and the relative accuracy with which superior genotypes can be identified in low- and high-input environments, and (c) predicting the direct and indirect responses to selection at each input level. On the basis of published data, it seems feasible to develop corn hybrids specifically adapted to production with lower rates of N application than are now commonly used in the United States.

Many farmers are turning to organic or “low input” farming as a strategy for economic survival. Several comparisons of actual grain farms in the central and northern states showed that organic farming equals or exceeds conventional farming in economic performance. These findings are supported by studies that used yield data from research plots as inputs to economic models. However, models that relied more heavily on hypothetical data showed an economic disadvantage for organic farming. This may have been a result of the failure of the hypothetical models to incorporate valid assumptions on conservation and efficient utilization of water, nutrients, fuel, labor, and capital. Established organic farmers are less vulnerable to natural and economic risks than conventional farmers because their systems are more diversified. They also are less able, however, to take advantage of income tax deductions. Future trends in commodity prices, input prices, pollution regulation, and research can be expected to have mixed effects on conventional and organic farmers, but the net impact will probably favor organic farmers. On a macroeconomic (i.e. national) scale, conversion to organic farming would have many benefits. It would reduce federal costs for supporting commodity prices, reduce depletion of fossil fuels, reduce the social costs associated with erosion, improve fish and wildlife habitats, and insure the productivity of the land for future generations. However, widespread conversion to organic farming would have an undesirable impact on the balance of trade. Future research on the economics of organic farming at the farm or microeconomics level should be directed at horticultural crops, southern latitudes, marketing, and the process of conversion from conventional to organic farming. Future macroeconomic research should quantify the social benefits described above, enabling decision makers to compare organic farming with other policy options.

The development of political strategies in Canada to support the transition from conventional to sustainable agriculture has been limited by the absence of a comprehensive conceptual framework for identifying the most critical policies, programs, and regulations. In this paper, we propose a framework that uses an efficiency/substitution/redesign spectrum to categorize both sustainable fanning systems and government activities. The framework is then used to identify a diverse range of short, medium, and longterm strategies to be pursued by governments in Canada to support the transition. Strategies discussed include research, diffusion, and training; market development; and safety net programs and tax provisions. Finally, the implications and implementation of the redesign concept for food production, processing, and distribution are outlined.

Recently there has been a change in thinking among many agricultural leaders and researchers toward a major focus on agricultural sustainability. To make progress toward such sustainability requires a clear delineation of its concepts and components. In this paper, I attempt to clarify relevant concepts and terminology in an effort to facilitate communication and cooperation. I also recognize, however, the intense feelings involved in these definitions. More satisfactory definitions will come in time as research and practice continue.

Potato acreage and total production in Maine have declined steadily since the 1960s. In 1991, a University of Maine research team established a large-scale, long-term, comparative study of three factors that form the foundation of productive potato cropping systems: soil management, pest management, and variety choice. This study, the Potato Ecosystem Project, included 96 main plots (5.8 ha total) and near-by “component studies.” The project contrasted amended vs. unamended soil management strategies; conventional vs. reduced-input vs. bio-intensive pest management strategies; and disease and stress susceptible vs. tolerant potato varieties. Given recent concerns over resistance to pesticides and increasing costs of agricultural chemical inputs, the reduced-input and bio-intensive pest management systems provided encouraging results. Weed growth was similar in the conventional and reduced-input systems. Colorado potato beetle thresholds were exceeded less often and their densities were lower in the bio-intensive system than in the reduced-input and conventional systems. Lady beetles, which are major aphid predators, were more abundant in the bio-intensive pest management system compared with the reduced-input and conventional systems in 5 of the 6 years. Tuber yield and quality were maintained at a high level in the reduced-input system, although difficulties with plant disease, nutrient and weed management contributed to significantly lower yields in the bio-intensive pest management system. Economic analysis indicated that from 1993 to 1996, the reduced-input system had a greater return over variable cost (avg. $973 ha-1) than the conventional (avg. $890ha-1) and bio-intensive pest management systems (avg. $578ha-1). The amended soil management system achieved rapid improvements in soil quality: soil organic matter, water stable aggregates, potassium, and soluble inorganic phosphorus contents increased while requirements for synthetic fertilizers were reduced. These improvements in soil quality enhanced late-season crop vigor, canopy duration and tuber quality, and increased yields by 13% and 30% over the unamended system in 1994 and 1995, respectively, but not in 1996. Improved crop vigor in the amended soil management system also benefited weed control efforts by encouraging a more weed-suppressive potato crop. In the biointensive pest management system, in which weeds were controlled mechanically, the amended soil management system had less weed biomass than the unamended soil management system in 1994 and 1995. Conversely, the amended soil management system consistently increased flea beetle populations and, in one of two years, the incidence of Rhizoctonia. The choice of potato variety also affected pest dynamics. Total aphid density (all aphid species considered together) and almost all disease ratings were higher on ‘Superior’ than ‘Atlantic’ potato.

Results of calculations on the economic potential for alternative (low input, sustainable) farming systems in a small grain-row crop region of the Northern Plains are reported. Two sets of alternative farming systems, in which no chemical fertilizers or herbicides are used, are compared with various conventional and reduced till systems. In Farming Systems Study I (FSS1), an alternative rotation consisting of oats, alfalfa, soybeans, and corn is compared with conventional and ridge till rotation systems composed of corn, soybeans, and spring wheat. In Farming Systems Study II (FSS2), three systems with an emphasis on small grains are compared. An alternative system rotation consisting of oats, sweet clover, soybeans, and spring wheat is compared with conventional and minimum till rotation systems comprised of soybeans, spring wheat, and barley. Results of baseline economic analyses show that alternative farming systems can be competitive with more conventional systems in at least some situations. The alternative systems entail markedly lower direct costs, and the alternative system in FSS2 has approximately the same net returns as the comparable conventional and minimum till systems. The FSS1 alternative system has positive but somewhat lower net returns than the comparable conventional and ridge till systems. Sensitivity analyses were conducted with alternative system crop yields, chemical fertilizer and herbicide prices, and varying assumptions about future Federal farm program support levels and acreage set aside requirements. The yield sensitivity analyses show that one alternative farming system requires yields about 5–10 percent above those of the comparable conventional system to produce the same net returns. However, the other alternative system is competitive with a conventional system even with yields 5 percent lower. Analyses varying chemical fertilizer and herbicide prices reveal that the alternative farming system in FSS1 becomes competitive with more conventional systems when fertilizer and herbicide prices rise by 50 percent. The alternative farming system in FSS2 is already competitive at current fertilizer and herbicide prices. In some cases, sensitivity analyses with Federal farm program provisions indicate that reductions in farm program benefits increase the economic competitiveness of alternative farming systems. However, important exceptions occur. Results indicate that not only the level of future farm program benefits, but also the form of program provisions and compliance requirements, will affect the relative competitiveness of alternative farming systems.

Residues of dead cover crops can suppress weeds by providing a mulch on the soil surface. The cover crop usually is killed with herbicides, but a mechanical method is desirable in systems intended to reduce chemical use. We designed and built an undercutter to kill cover crops by severing their roots while flattening the intact aboveground biomass on the surface of raised beds. We studied which cover crop species could be killed with the undercutter and compared the weed control potential of cover crop residues after flail mowing, sicklebar mowing, and undercutting.

Whether a species was killed by the undercutter depended primarily on growth stage. Species that were in mid- to late bloom or beyond, including rye, hairy vetch, bigflower vetch, crimson clover, barley, and subterranean clover, were easily killed by undercutting. There were no differences in dry weights of broadleaf weeds between the undercut and simulated sicklebar mowed treatments, both of which had less weed biomass than the clean-tilled or flail-mowed plots.

Modern large-scale conventional agriculture with intensive monoculture and row-cropping practices often results in unacceptable soil erosion and runoff and in associated losses of nutrients and pesticides. It also adversely affects wildlife. Sediment from erosion is the greatest pollutant of surface water in the United States and is a major carrier of agrichemicals into the water system. Conservation tillage practices can significantly reduce soil losses in modern production systems, but pollution of surface and groundwaters from runoff and associated potential for increased use of pesticides may still present a hazard. Erosion can be reduced to tolerable levels by the use of crop rotations, meadow crops, and mulch tillage, as commonly used in alternative agriculture. These cultural practices also result in diversity in crop types and in smaller fields, with possible benefit to many wildlife species. Chemical threats to the environment and to wildlife are reduced because synthetic chemicals are used sparingly or not at all.

Cultivars vary considerably in how they respond to moisture stress throughout crop development. In areas of the Pacific Northwest with less than 250 mm of annual rainfall, win ter wheat is under moisture stress most of the time from planting to harvest. Cultivars must be ab le to absorb moisture, germinate, and emerge under high temperature, poor seed zone moisture, and deep seed cover. Moisture stress slows emergence and seedling development and reduces most yield components, including number of tillers, seeds per spike, seeds per unit area, seed size, and seed weight per unit volume. Additionally, leaf senescence and maturity are earfy under moisture stress conditions. A cultivar cannot obtain its potential yield with less than adequate moisture; therefore, under moisture stress fewer tillers and seeds are produced. Which plant structures are reduced is determined by the growth stage of the plant during stress, while the extent of this reduction is determined by the severity of moisture stress and the genotype of the cultivar.